Aeronautical propeller



Oct. '14, 1930. s. A. REED AERONAUTICAL PROPELLER Filed March 20, 1929 Patented Oct. 14, 1930 UNITED STATES PATENT OFFICE SYLV ANUS A. REED, OF NEW YORK, N. Y., ASSIGNOB TO THE REED PBOPELLEB O0.

, 1110., 01' NEW YORK, A. CORPORATION 01' NEW YORK AEBONAUTICAL PBOPELLEB Application filed larch- 20, .1989. Serial 10. 848,587.

My invention relates generally to aeronautical propellers and especially to those having thin solid metal blades, either integral with the hub or detachable and which may be 5 adjustable in pitch, and has for its object a reduction of weight, in a manner avoidlng the usual composite or hollow construction hitherto employed for such reduction in weight, and which type of construction [0 usually has a plurality of parts joined together.

Such reduction in weight is especially important when a heavy material, such as steel, is utilized for propeller blades. In avoiding composite construction, I use solid blades and I have invented means for lightening,

I or reducing the weight at certain portions of the blades, without impairing their strength and permanence of form, so that I obtain .9 finally a blade or propeller of steel weighing not materially more than a normal blade or propeller made of aluminum alloy, which type has come into large use, based upon my inventions set forth in my U. S. Letters Patent Nos. 1,463,556 and 1,518,410, granted July 31, 1923, and December 9, 1924. respectively.

Hollow blades usually have front and back metal sheets or plates welded together at or near their edges, making joints, which are so not free from objections, and especially is it diflicult therewith to obtain the most desirable degree of thinness at or near the blade tips. In my present invention I make a propeller :5 or blade which is structurally integral and solid, and I lighten the weight by providing a plurality of holes or recesses, not impairing the strength or stifiness required for the blade, and such recesses or holes are covered 40 with thin and preferably light-weight material, or filled partly or wholly with lightweight material, adapted to restore the continuity of the blade face, but which covering or filling means do not contribute to the structural integrity of the blade or propeller.

In the following description and claims I use the word root to designate the part of the blade from the hub to about one-fifth blade radius, the term shank from about one-fifth to two-fifths blade radius, and the word flare from about two-fifths to fourfifths, and the word tip for the remaining one-fifth. Most of the propulsion of a blade is rendered by the flare and tip, but a large percentage of the total weight is in the hub, root and shank. I prefer, therefore, to leave the outer half of the flare and entire tip portions normal and without lightening holes or recesses, and to have all such holes or recesses confined to the inner half of the flare, the root and the shank. In the latter regions surface irregularities have the least deleterious effect, and furthermore as the centrifugal force in this region is far less than in the flare and tip regions, the matter. of firm attachment of the covering accessories is less diflicult.

I have illustrated types of my invention in the accompanying drawings, wherein:

Figure 1, shows a plan view of a solid single-piece metal propeller embodying my invention. and with one of the blades partly broken away; the recesses being shown open.

Figure 2, shows a side view of the pro 'eller shown in Fig. 1, but with the recesses c osed.

Figure 3, shows a plan view of a detachable blade propeller embodying my invention and with one of the blades broken away.

Figure 4. shows several cross sectional views of the blade shown in the previous figures, with the weight-reducing excavations uncovered and unfilled.

Figures 5 to 9, show enlarged cross-sectional views of several different means for covering or filling the weight-reducing excavations.

Figure 10, shows 0. Ian view of a portion of a blade having an elbngated or slot shaped weight-reducing excavation, with its closure means.

Figure 11, shows a cross-sectional view of a blade with channeled weight-reducing excavations.

Figure 12, shows a. plan view of a portion of a blade having its excavations covered by an enveloping sheet'of metal.

Figure 13 shows a cross-sectional view of a blade embodying the modified form of structure shown in Fig. 12.

Referring to the drawings,-the propeller shown in Figs. 1 and 2, comprises blades 1 and 2, with an integral hub 3, the blades being solid and the entire propeller is forged hot between steel dies, preferably from alloy steel, having high tensile strength, elasticity and fatigue limit, but it may also be made of other forged or rolled metal alloy, such as strong alloys of aluminum or magnesium. In die hot forging this propeller from a single bar of alloy steel, the root parts are set at appropriate pitch angles in such forging, but the parts beyond the roots are not dietwisted and these parts are subsequently twisted to appropriate pitch angles.

In the construction shown in Fig. 3, the blades 1, 2, are solid and are detachably and adjustably mounted in a separate hub 3, in any of the well known ways.

Taking a propeller so made of nine-feet iameter, an example, I prefer to then #:cavate the inner blade end portions by Irilling two rows of holes or recesses, as ,hown and 5, either entirely through the blades, as shown in Figs. 4. 5, 8, 11, 12 and 13, or partly through, as shown in Figs. 6, 7 and 9, in which the holes are drilled in preferably from the driving faces of the blades. The open ends of the holes or recesses'4 and 5, are then covered or filled in any suitable manner, and preferably in some of the ways shown in the difierent figures of the drawings, thereby restoring the smooth surface of the blade, and preventing loss of efiiciency, which would result from leaving these excavations uncovered.

It is to be noted that the longitudinally extending lines of the circular perforations or recesses 4 and 5, are so chosen and disposed as to leave an unperforated central rib 6, and two edge or marginal ribs 7 and 8. In the line of perforations or recesses, the removed metal would not have contributed materially towards resistance against radial tensile stresses, which are mainly due to centrifugal force. and which in a propeller of this will be probably over fifteen tons. the central and edge ribs, 7 and 8, being continuous and unbroken, are figured at each radius so as to retain a cross-section in the aggregate adequate to sustain, with a large of safety, the entire estimated radial stresses without the assistance of the metal line of the holes or recesses.

The resistance of the blade to torsional stresses to change the pitch angles will depend upon the blade shape, and in order to get the maximum thinness in the flare and tip portions, and yet to avoid blade flutter, the most favorable form includes asteady spread or increase or expansion in thickness or outside over-all dimensions in the shank, and .this form in a solid blade would result in excessive weight in certain cases. But by my invention of lightening excavations in the root and shank of a solid blade, I retain this favorable spread in the root and shank, without an excessive weight. As intimated, the flare and tip portions are made as light as it is possible to make them by reducing the camber ratio to the minimum for stability of pitch. Such minimum camber ratio will be found to give a large surplus of cross-sectional area to sustain tensile and bending stresses.

In order to further lighten the root and shank portions of the blade, I may provide channels or slotted recesses or grooves in one or both faces of the blade. as shown in Figs. 3, 11, 12 and 13, at 9. I prefer to have these channels in addition and supplementary to the circular perforations or recesses 4 and 5, and to have substantially the same diameter and to include a plurality of the circular recesses which lie in a single longitudinal row. I prefer to carry the said channels only partly through the blade thickness, either all from one face, or partly from one face and partly from the other, and in each case leaving about one-fifth of the blade thickness intact, and forming a web element 10, serving to stiffen the blade. This is shown in detail in Figs. 11 to 13, Fig. 11, being a cross-section on line ab, in Fig. 3, and Fi 13, being a crosssection on line Z-m, in ig. 12.

The cross-sections shown in Fig. 4, are indicated by the lines 0-d; ef; g--h and i-Jc, respectively, in Fig. 1.

To restore the surface of the blade faces where the excavations occur, I may utilize one of several means. Fig. 5,-illustrates, is cross-section one of said means in which a circular recess or hole 4, is provided with an internal screw-thread into which is screwed a threaded plug 11, of wood or other lightweight material, and this plug may if deslred be additionally secured in place in any well known manner. In Fig. 6, I illustrate a circular recess 4, carried partly through the blade from one face, but leaving the opposite face unbroken, and the open end of the recess closed by a plate of metal 12, with externally threaded flange adapted to be screwed into the interior thread in said recess far enough to leave a flush surface to the blade. The said closure plate is preferably bulged on the inner face, as shown at 13, in order to obtain strength with lightness.

In Fig. 7 I show in cross-section a similar recess 4, to that of Fig. 6, but with the open end closed with athreaded disc of wood 14,

screwed into the threaded recess, and preferably concave on its inner face at 15, to obtain strength with lightness.

Fig. 8, shows a cross-section of the blade with a circular or other shaped recess 4, closed at each end by a disc or plate of metal 16, having retracted edge flanges fitting angular flares 1n the edges of the recess and bringing the outer surfaces of the discs flush with the blade faces. Each disc 16, has a countersunk or depressed portion 1?, erforated centrally, and 18, is a rivet or be t with nut uniting opposite pair of covers or plates, the heads of the rivet or bolt lying in the countersunk depressions in the discs orclosure plates, so as to be flush with the blade faces.

Fig. 9, shows a cross-section of the blade with a depression or recess 4, carried partly through from one face to within a short distance of the other face. The recess has a shouldered edge at 19, and 20 is a metal cover plate fitting, closely into the mouth of the recess against the shoulder leaving a slight interspace at 21. The plate is then welded at the edges to the shoulders of the recess, the welding material filling the interspace, and the outer surface of the closure plate being flush with the blade face. The crosssection of the closure plate is bulged on the inner surface to obtain strength with light-' ness.

Fig. 10 illustrates a longitudinal recess 4, considerably elongated as indicated in dotted lines, with a closure plate 22, shown in full lines, the cross-section being substantially the same as in Fig. 9, the plate being bulged on the inner surface and preferably welded into the mouth of the recess against the shoulder therein, as in Fig. 9.

Figs. 12 and 13, show means of closing the surface openings caused by the holes or recesses so as to restore the blade surface and the same consists in a thin sheet of metal, or other suitable material, 23, enveloping the entire blade in the re 'on occupied by said recesses. This enveldping sheet is disposed transversely around the blade and has its overlapping edges united by welding or riveting or other well known means, the screws 24 also servingto hold the edges together, and

passing into the body of the blade. I prefer to anchor said closure sheet to a fixed place on the blade, by means of rivets or bolts 25, passing through the entire blade, and having their heads lying in countersunk de ressions 26, so as to leave a flush surface to t e blade. The said rivets or bolts will bear against the 1 sides of the recesses in such a manner as to the originally impressed blade twist will also be unyielding.

The preservation of continuous medial and edge ribs in the roots and shanks of the blades of my invention, while at the same time removing much of the mass of the root shank insures stability of blade pitch, although the material intermediate of the me dial and edged ribs has been largely removed or omitted by the lightening recesses or excavations. On the other hand, the webs 10, left between the holes contribute in'a valuable manner toward bracing the medial and edge ribs, and assistin in providing for the flare and tip parts a support with spread adequate to insure the latter portions against tendency to vibrate during operation.

It will be noted from the illustrations and description that the closure plates, or light plugs or enveloping sheet, do not contribute structurally to the integrity, strength or stability of the blades. That is to say, except for the probably deleterious effect of these excavations upon good performance flight, in case the excavations were not covered flush with the blade surface, nevertheless, the blades, without the covers or plugs would be structurally complete and adequately resistant for the purposes of flight. This novel feature is in contrast to the usual device of a hollow metal blade made of more than one continuous sheet of metal, namely, two or more such sheets share in the structural integrity of the blade, and the removal of one would materially impair the strength of the blade. In case of a hollow blade made from a tapered tube, flattened to blade profile, there are structural disadvantages at the edges and tips of the blades.

I do not confine m self to any special means of restoring the lade surface where a lightening excavation has been formed. In using elongated recesses, the result is that of fiuting so that the necessary strength is pre' served while the weight is reduced.

, It will be understood that I do not confine myself to the specific forms of structures herein set forth, as modifications may be made in the several different parts thereof, without, however, departing from the spirit of my invention.

Having thus described my invention, what I claim and desire to secure by Letters Pat-' ent is:

1. In an aeronautical propeller, an integral solid blade of operative profile, the blade, throughout the inner end portion of its length, having formed therein one or more surface excavations of shape to provide for a maximum of weight reduc tion consistent with retaining in o blade adequate cross-sectional area to s tain, during flight, the radial ten due to centrifugal force; and a. lightw ht "-r III - surface restoring means associated with said excavated blade portion.

2. In an aeronautical pro eller, an integral I solid blade comprising a re atively heavy inner' end portion and a relatively light outer end 'portlon, said outer end ortion having a minimum camber ratio consistent with torsional'stability durin flight, and said inner end portion having ormed therein one or more surface excavations of such size and shape as to provide for a maximum of weight a reduction consistent with-retaining in the inner end portion ofthe blade adequate crosssectionalarea to safely sustain, during flight,

the radial tensile stresses due to centrifugal force.

8. In an aeronautical pro eller an integral solid blade comprising a re ative y heavy inner end portion and a relatively light outer end portion, said outer end portion having a minlmum camber ratio consistent with torsional stability during flight, and said inner endportion having ormed therein one or,

more surface excavations of such size and shape as to provide for a maximum of weight reduction consistent with retaining in the inner end portion of the blade adequate crosssectional area to safely sustain, during flight,

I the radialfgtensile stresses due to centrifugal force; andfa light weight surface restoring means associated with said "excavated blade portion.

4. In an aeronautical pro eller an integral solid blade comprising a re atively heavy in-v sional stabilit formed therein one or more surface excavations of such size and shape as to provide for a maximum of wei ht reduction cons stent w1th retalmng in sa1d mner end ortlon adeuate cross-sectional area to sa ely sustain,

uringuflight the radial tensile stresses due to centri gal force; and a' light weight nonstructural surface restoringmeans associated with said inner end excavated blade portion.

5. In an aeronautical propeller, an integral S0lld blade comprising a relatively heavy root and shank portion and a relatively light flare and tip portion, said tip portionand a substantial portion of said flare portion having relatively smooth exterior surfaces as well as-a minimum camber ratio consistent with torsional stability during flight, and said root and shank portions having formed therein one or more surface excavations of such size and sha e as to provide for a maximum of wei ht r uction consistent with retaining in the lade adequate cross-sectional area to safelysustain, durin flight, the radial tensile stresses due to centrifugal force; and a light surfaces thereof are made. substantially smooth.

6. In an aeronautical propeller, an integral solid blade of operative profile, the blade,

' throughout the inner end portion only of its length, having formed therein one or more sur ace excavations of such size and shape as to provide for a maximum of weight reduction consistent with retaining in the blade adequate cross-sectional area to safely sustain, during flight, the radial tensile stresses due to centrifugal force; and a li ht-weight surface restoring means associate with said excavated blade portion.

7. In an aeronautical propeller,an integral solid blade of operative profile, the blade, throughout the inner end portion of its length having formed therein two substantially parallel longitudinally extending excavations of such width and depth as to provide for a maximum of weight reduction consistent with retaining in the blade adequate cross-sectional area to safely sustain, during flight, the radial tensile stresses due to centrifu al force, said strength-giving inner end bla e portions being extended longitudinally of'the blade in line with its lon itudinal axis and along its opposite longitudinal edges respectively.

8. In an aeronautical propleller, an integral of and solid bladehavin 1n t e inner thir its radius a weight re ucing excavation leaving adequate cross-sectional area to withstand, unaided, the radial tensile stresses due to centrifugal force, the outer third radius of the blade being unexcavated tho of minimum camber ratio consistent with torsional stability during flight, and a .light weight nonstructural surface restoring means associated with said inner excavated portion of the blade length.

9. In an aeronautical propeller, a blade integral and solid from end to end, said blade throughout substantially the outer third of its length having a minimum camber ratio consistent with torsional stability in flight, and throughout substantially the inner third of its length having excavations formed in its exterior surface to materially reduce its overall weight, the excavations bein of such'size and sha e as to insure at all points throughout the blade length sufiicient bulk of material to adequately withstand the radial tensile stresses due to centrifugal'force.

10. In an aeronautical propeller, an integral solid blade having in its opposite faces weight reducing excavations, said excavations being confined to the inner two-thirds of the blade length and said excavated. blade portion having adouble-I cross-section in.

which the outer flanges are at the blade edges and the middle flange is substantially at the longitudinal blade center, and in which the connecting webs operate to stiffen the structure where the excavations occur.

11. An alloy steel aeronautical propeller blade, solid and integral from end to end and 5 reduced in weight sufiiciently to render it operative and safe by excavations formed in its outer surface, the excavations, in every instance, being confined to the inner two-thirds of the blade length.

Signed at New York city, in the county of New York and State of New York, this 15th day of March, 1929.

SYLVANU S A. REED. 

